1. Field of the Invention
The present invention relates to a passive Radio Frequency Identification (RFID) reader and a method for controlling operation of reading tag information in the RFID reader; and, more particularly, to an RFID reader that can minimize collision among RFID readers in an environment where there are a plurality of RFID readers within a limited operating environment by making each RFID reader select a channel at different delay time based on random value, and a method for controlling operation of the RFID reader.
2. Description of Related Art
In general, Radio Frequency Identification (RFID) is a technology for recognizing, tracing, and managing human beings, animals, and/or objects with a tag attached thereto by writing or reading information in or out of a tag having its own identification information without a contact.
An RFID system includes a plurality of electronic tags, or transponders, which will be simply referred to as tags hereinafter, and an RFID reader. Each tag has identification information and it is attached to an object or an animal, and the RFID reader writes or reads information in or out of the tags. RFID systems are divided into a mutual induction type and an electromagnetic wave type according to the communication method between the RFID reader and the tags.
The RFID systems are also divided into an active type and a passive type according to whether the tags are operated with their own power source. They are also divided into a long wavelength RFID reader, an intermediate wavelength RFID reader, a short wavelength RFID reader, an ultra short wavelength RFID reader, and a microwave RFID reader. Diverse specifications are defined or under definition according to the above classification.
Passive RFID wireless equipment used in Korea is defined to perform access in a channel bandwidth of 200 kHz in the range of 908.5 to 914 MHz by using a Frequency Hopping Spread Spectrum (FHSS) or Listen Before Talk (LBT) frequency occupying method. The FHSS frequency occupying method randomly shifts a frequency band to another using the frequency bands of multiple channels for interference avoidance.
The FHSS frequency occupying method was selected by the United States who has a wide frequency band to use. The LBT channel occupying method searches an available channel before transmitting data to share frequencies. If the available channel is searched, the data is transmitted through the searched channel in the LBT channel occupying method, only when the channel is vacant. The LBT channel occupying method is selected as a standard channel occupying method in Europe who has a narrow frequency band to use.
In South Korea, the number of channels for an RFID system is limited to 27 in a bandwidth of 5.5 MHz. Thus, more channel regions are allocated to the LBT channel occupying method than to the FHSS method. According to the LBT channel occupying method, an RFID reader senses the occupancy status of a channel and, only when the channel is vacant, an RFID reader transmits commands to a tag. Therefore, the RFID reader of the LBT method should not only have a high reception performance but also be able to sense the occupancy status of a channel. In a case where a conventional LBT method is used, the structure of an RFID reader becomes complicated. Also, although the number of RFID readers is relatively smaller than other regions, the channel should be able to be sensed necessarily.